Although I missed the earlier post to which Judith Neulander was responding, may I add a bit to her wide-ranging summary of the tendency of European Christians to label the "others" whose lands they colonized as remnants of the "losts tribes"?
As early as Torquemada, European Christians hypothesized that the natives of the "New World" might be descendents of the "lost tribes" of Israel. This notion, apparently widely discussed by Spanish intellectuals, had spread to England by the early 17th century. It was referred to by William Wood in _New England's Prospect_ (1634) and circulated in manuscript by Thomas Thorowgood entitled "Jews in America, or Probabilities that the Americans are of that Race" -- citing Roger Williams as a source! This manuscript was printed in 1650 together with an account by Antoine Montezinos of a community of "Jews" he had found living in Peru (and reciting the _Shema_!!).
Montezinos had already told his story to Manasseh ben Israel, rabbi of Neveh Shalom (Amsterdam) and a prominent scholar and publisher. Manasseh was sufficiently intrigued to have Montezinos take an oath on his story's authenticity; an affidavit was executed before the chief rabbi of the Amsterdam synagogue. A copy of that affidavit was published as an appendix to Thorowgood's treatise when it was printed in 1650. Like Torquemada and his Spanish successors, both Wood and Thorowgood were interested in the "origin" of the natives of the "Americas" because of the light it shed on how best to convert them to Christianity. Manasseh's interest was of course different and in 1650 he published his own account of Montezinos' story together with his own conclusions under the title _The Hope of Israel_. Its dedication (to the republican English Parliament) like its timing was not coincidental.
Part of Manasseh's goal was to encourage Oliver Cromwell and his comrades to allow the return of Jews to England. Allying themselves with the American "descendents of the lost tribes" and their European cousins would offer the English republicans certain obvious advantages vis a vis the Spanish. The influence of Rabbi Manasseh ben Israel's _Hope of Israel_ is evident -- it went through through several editions before 1700. Others, of course, countered the "Jewish" origins of the Americans and the debate continued . . . .